The bug

Zombified Piglins stopped spawning near light sources in the nether. This bug affects gold farm by reducing the amount of valid spawning positions.

To test it, I created spawning platforms in the nether (high above the nether ceiling, see screenshot). The only possible spawning block were on the platforms. Two platforms were empty, a third platform had torch rows on every second block, a fourth platform had glowstone rows two blocks above the platform. A fifth platform was made out of Magma Blocks.

The results show, that piglins can spawn on the first two platforms and the fifth platform. On the platforms with the torches and the glowstone above, no zombified piglins spawned.

Recreating this setup in 1.13.2 shows that piglins can spawn on all platforms.